Problem Statement:
Zip two lists of Integers.
If the lists are of unequal length, return None; otherwise return Some of (int*int) list.
Solution:
Following naïve solution recurses over elements of the lists, and creates tuple, as part of the zip operation. If both lists are empty, it returns Some [].
| let rec zipTwo (x:int list) (y: int list) : ((int*int) list) option = | |
| match x,y with | |
| | ([], []) -> Some [] | |
| | (xhd::xtl, yhd::ytl) -> | |
| match zipTwo xtl ytl with | |
| | None -> None | |
| | Some lst -> Some ((xhd,yhd)::lst) | |
| | (_,_) -> None |
The unequal length case is handled by the pattern outlined in line 8 , which simply returns None. Subsequent return calls of the recursion detect it and simply return None.
Thus, resultant signature of zipTwo is given by:
| val zipTwo : x:int list -> y:int list -> (int * int) list option |
Output:
| > zipTwo [] [];; | |
| val it : (int * int) list option = Some [] | |
| > zipTwo [1;2] [2;4;8];; | |
| val it : (int * int) list option = None | |
| > zipTwo [1;2;3] [2;4;8];; | |
| val it : (int * int) list option = Some [(1, 2); (2, 4); (3, 8)] |
